Furo[2,3-c]pyrazole compounds were first synthesized by two of the present inventors, L. J. Haung and S. C. Kuo, and H. T. Li in an article published in J. Taiwan Pharm. Assoc. 31 (1), 47-55 (1979). Ethyl 3-methyl-1-phenylfuro[2,3-c]pyrazole-5-carboxylate (3) was synthesized in this article. As shown in the following Scheme 1, chloro-3-methyl-1-phenylpyrazole-4-carboxaldehyde (1) and ethylglycolate (2) were condensed to form ethyl 3-methyl-1-phenylfuro[2,3-c]pyrazole-5-carboxylate (3); or 5-hydroxy-3-methyl-1-phenylpyrazole-4-carboxal-dehyde acetate (4) was reacted with ethylbromoacetate (5) to obtain the ethyl 3-methyl-1-phenylfuro[2,3-c]pyrazole-5-carboxylate (3). The product produced by these two methods are very low in yield and stability. Therefore, only one furo[2,3-c]pyrazole compound (3) was synthesized and no further investigation was conducted in the above-mentioned article. ##STR1##
The compound (3) as described above is in the class of N.sup.1 -substituted furo[2,3-c]pyrazole compounds having the formula (A). As to N.sup.2 -substituted furo[2,3-c]pyrazole compounds having the formula (B) have not yet been reported in any literatures. ##STR2##